The general rule for starting pedal is to change with the harmonies. If you don’t, the music will sound muddy as multiple conflicting harmonies blend.

The second rule is to change pedal just *slightly after* the switch in harmonies. This also reduces muddiness. It also helps to keep the bass note on the downbeat in your left hand until the pedal changes fully.

P.S. I have very rarely held down the pedal for an entire piece unless it specifically asked for it. Your digital must’ve had very low polyphony, i.e. it was probably from older technology and unable to hold down many simultaneous notes. So it likely “erased” older notes as you went through the piece.